DESCRIPTION Disease and old age are associated in the heart with high frequencies of mutations in mitochondrial DNA (mtDNA). Mutation levels can be up to several hundred fold greater than normal in patients with ischemic heart disease, cardiomyopathy, and graft vascular disease in the transplanted heart. In older subjects with no apparent disease, levels may climb to several thousand times that seen in young individuals. As impressive as those increases are in mutation frequencies, the critical question is whether they contribute either to the pathophysiology of disease or to the decline in mitochondrial respiration that occurs with aging in the heart. The answer to that question is unknown, in part, because mutation frequencies in absolute terms are usually relatively low -- often less than 1 percent of the total population of mtDNA molecules. Since nearly all data on mtDNA mutations in the heart are correlative, their association with disease and with aging can be interpreted as a molecular consequence of the pathophysiology rather than as a contributing factor. The applicant's goal is to determine the physiological importance of elevated mtDNA mutation frequencies in the heart. He will construct transgenic mice in which mtDNA mutations accumulate at an accelerated rate with age. These mice will contain a transgene that expresses a mutant form of the mtDNA polymerase which lacks proofreading. Since the mammalian mtDNA polymerase (DNA pol gamma) appears to have no role in nuclear DNA replication, mice expressing the mutant transgene are predicted to show decreased fidelity of only mtDNA replication. The decreased fidelity will lead, in turn, to an accelerated accumulation of mtDNA mutations in the transgenic mice. With this model the investigator will ask whether mtDNA mutations have physiological consequences at the levels found in cardiac disease and with aging. He will characterize the effects on mitochondrial respiration of an increasing level of mtDNA mutations and determine the effects of elevated levels of mtDNA mutations on cardiac function and oxidative stress in the heart.